Flame-retardant thermoplastic polyurethane

ABSTRACT

The present invention relates to compositions comprising at least one thermoplastic polyurethane, at least melamine cyanurate, at least one first phosphorus-containing flame retardant (F1) selected from the group consisting of alkyl esters of phosphoric acid and alkyl esters of phosphonic acid, where the alkyl radicals are selected from C1 to C12 alkyl radicals, and at least one further phosphorus-containing flame retardant (F2) selected from the group consisting of derivatives of phosphinic acid, and to the use of such a composition for production of cable sheaths.

The present invention relates to compositions comprising at least onethermoplastic polyurethane, at least melamine cyanurate, at least onefirst phosphorus-containing flame retardant (F1) selected from the groupconsisting of alkyl esters of phosphoric acid and alkyl esters ofphosphonic acid, where the alkyl radicals are selected from C1 to C12alkyl radicals, and at least one further phosphorus-containing flameretardant (F2) selected from the group consisting of derivatives ofphosphinic acid. The present invention further relates to the use ofsuch compositions for production of cable sheaths.

Cables produced from PVC have the disadvantage of evolving toxic gaseson combustion. Therefore, products based on thermoplastic polyurethanesare being developed, these having lower smoke gas toxicities and havinggood mechanical properties, abrasion resistance and flexibility. Becauseof the inadequate flammability performance, compositions based onthermoplastic polyurethanes are being developed, these comprisingvarious flame retardants.

Flame-retardant thermoplastic polyurethanes find use particularly incable production as cable sheaths. A common requirement here is for thincables having thin cable sheaths which both pass the relevant flametests (e.g. VW1) and have adequate mechanical properties.

In these cases, it is possible to add both halogenated and halogen-freeflame retardants to the thermoplastic polyurethanes (TPUs). Thethermoplastic polyurethanes comprising halogen-free flame retardantsgenerally have the advantage of evolving less toxic and less corrosivesmoke gases when burnt. Halogen-free flame-retardant TPUs are described,for example, in EP 0 617 079 A2, WO 2006/121549 A1 or WO 03/066723 A2.US 2013/0059955 A1 also discloses halogen-free TPU compositionscomprising phosphate-based flame retardants.

US 2013/0081853 A1 relates to compositions, preferably halogen-freeflame-retardant compositions, comprising a TPU polymer and a polyolefin,and also phosphorus-based flame retardants and further additives.According to US 2013/0081853 A1, the compositions have good mechanicalproperties.

Melamine cyanurate has also long been known as a flame retardant forindustrial plastics. It finds wide use especially in polyamides, butalso in polyesters and other plastics such as styrene-based polymers.For instance, WO 97/00916 A describes melamine cyanurate in combinationwith tungstic acid/tungstic salts as flame retardant for aliphaticpolyamides. EP 0 019 768 A1 discloses flameproofing polyamides with amixture of melamine cyanurate and red phosphorus.

According to WO 03/066723, materials comprising only melamine cyanurateas flame retardant, in the case of low wall thicknesses, have neither agood limiting oxygen index (LOI) nor good flame retardancy, determined,for example, by performance in a UL 94 test.

WO 2006/121549 A1 also describes materials comprising, as flameretardant, a combination of melamine polyphosphate, phosphinate andborate. These materials do attain high LOI values at low wallthicknesses, but do not attain good results in the UL 94 test.

There are also various known thermoplastic polyurethanes which comprise,as flame retardants, combinations of melamine cyanurate in conjunctionwith phosphorus compounds. EP 0 617 079 A2 and DE 102 24 340 A1 disclosematerials that exhibit good performance in the UL 94 test (particularlyin the UL 94V test), but at the same time have low LOI values.

For example, materials which comprise, as flame retardants, combinationsof melamine cyanurate with phosphonic esters and phosphonic esters havegood results in UL 94V tests, but very low LOI values, for example <25%.Such combinations of melamine cyanurate with phosphoric esters andphosphonic esters are inadequate as flame retardants particularly in thecase of sheaths of thin cables. For various flame retardancyapplications, a high LOI value is required in standards, for example inDIN EN 45545.

By contrast, very high LOI values (>30%) can be achieved withcombinations of melamine cyanurate with phosphinates, but not goodresults in the UL 94V test. Corresponding materials are disclosed, forexample, by U.S. Pat. No. 6,207,736 B1, U.S. Pat. No. 6,255,371, U.S.Pat. No. 6,365,071 B1, U.S. Pat. No. 6,509,401 B1 and U.S. Pat. No.6,547,992 B1.

Accordingly, the compositions known from the prior art either do notexhibit adequate mechanical properties or have only inadequateflammability properties, for example flame retardancy and performance,in the UL 94V test.

PCT/EP2015/053192 discloses compositions comprising a thermoplasticpolyurethane, melamine cyanurate and a combination ofphosphorus-containing flame retardants. According to PCT/EP2015/053192,these compositions have the advantage of good flame retardancy combinedwith good mechanical properties and good chemical stability.

For many applications, however, good characteristics with regard todiscoloration under the influence of UV are also required. This isrelevant, for example, when materials are being used in construction invisible regions or cables that are exposed to insolation are beingsheathed.

Proceeding from the prior art, it was accordingly an object of thepresent invention to provide flame-retardant thermoplastic polyurethaneswhich have good mechanical properties, exhibit good flame retardancyproperties, simultaneously have good mechanical and chemical stabilityand additionally are discolored to a minor degree, if at all, whensubjected to UV irradiation.

According to the invention, this object is achieved by a compositioncomprising at least one thermoplastic polyurethane, at least melaminecyanurate, at least one first phosphorus-containing flame retardant (F1)selected from the group consisting of alkyl esters of phosphoric acidand alkyl esters of phosphonic acid, where the alkyl radicals areselected from C1 to C12 alkyl radicals and at least one furtherphosphorus-containing flame retardant (F2) selected from the groupconsisting of derivatives of phosphinic acid.

The compositions of the invention comprise at least one thermoplasticpolyurethane and also melamine cyanurate and a combination of twophosphorus-containing flame retardants (F1) and (F2).

It has been found that, surprisingly, the compositions of the inventionhave properties improved over the compositions known from the prior art,for example elevated flame retardancy and are especially discolored onlyto a minor degree, if at all, when subjected to UV irradiation.

The compositions of the invention comprise melamine cyanurate. It hasbeen found that, surprisingly, the compositions of the invention have anoptimized profile of properties as a result of the combination of thecomponents of the invention, especially for use as cable sheathing.

Melamine cyanurate in the context of this application is understood tomean, inter alia, all standard commercial and commercially availablesolid, preferably particulate, product qualities. Examples of theseinclude Melapur MC 25 (BASF SE) and Budit 315 (Budenheim).

According to the invention, melamine cyanurate is preferably used in theform of a 1:1 salt of melamine and cyanuric acid. The melamine excesshere is, for example, less than 0.2%, preferably less than 0.15%,further preferably less than 0.1%. According to the invention, thecyanuric acid excess is, for example, less than 0.25%, preferably lessthan 0.2%, further preferably less than 0.15%.

In the context of the present invention, it is likewise possible thatthe melamine cyanurate used has been treated, for example with anorganic compound. Corresponding materials are known in principle fromthe prior art.

The melamine cyanurate which is suitable in accordance with theinvention preferably consists of particles typically having a meanparticle diameter of 0.1 μm to 100 μm, preferably 0.5 μm to 60 μm, morepreferably 1 μm to 10 μm. The particle size distribution in the contextof the present invention may be monomodal or else multimodal, forexample bimodal.

In a further embodiment, the present invention therefore relates to acomposition as described above, wherein the melamine cyanurate has aparticle size in the range from 0.1 to 100 μm.

Melamine cyanurate is present in suitable amounts in the composition ofthe invention. For example, the proportion of melamine cyanurate in thecomposition is in the range from 20% to 40% by weight, based on theoverall composition, preferably composition in the range from 25% to 35%by weight, based on the overall composition, especially composition inthe region of about 30% by weight, based on the overall composition.

In a further embodiment, the present invention therefore relates to acomposition as described above, wherein the proportion of the melaminecyanurate in the composition is in the range from 20% to 40% by weightbased on the overall composition.

The sum total of the components of the composition is 100% by weight ineach case.

The composition of the invention further comprises at least onethermoplastic polyurethane. Thermoplastic polyurethanes are known inprinciple. They are typically prepared by reacting the components (a)isocyanates and (b) compounds reactive toward isocyanates and optionally(c) chain extenders, optionally in the presence of at least one (d)catalyst and/or (e) customary auxiliaries and/or additives. Thecomponents (a) isocyanate, (b) compounds reactive toward isocyanates,(c) chain extenders are also referred to, individually or collectively,as formation components.

In the context of the present invention, the isocyanates and compoundsreactive toward isocyanates which are customarily used are suitable inprinciple.

Organic isocyanates (a) used are preferably aliphatic, cycloaliphatic,araliphatic and/or aromatic isocyanates, further preferably tri-,tetra-, penta-, hexa-, hepta- and/or octamethylene diisocyanate,2-methylpentamethylene 1,5-diisocyanate, 2-ethylbutylene1,4-diisocyanate, pentamethylene 1,5-diisocyanate, butylene1,4-diisocyanate,1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophoronediisocyanate, IPDI), 1,4- and/or 1,3-bis(isocyanatomethyl)cyclohexane(HXDI), cyclohexane 1,4-diisocyanate, 1-methylcyclohexane 2,4- and/or2,6-diisocyanate and/or dicyclohexylmethane 4,4′-, 2,4′- and2,2′-diisocyanate, diphenylmethane 2,2′-, 2,4′- and/or 4,4′-diisocyanate(MDI), naphthylene 1,5-diisocyanate (NDI), tolylene 2,4- and/or2,6-diisocyanate (TDI), 3,3′-dimethyl diphenyl diisocyanate,1,2-diphenylethane diisocyanate and/or phenylene diisocyanate.Particular preference is given to using 4,4′-MDI.

In a further embodiment, the present invention therefore relates to acomposition as described above, wherein the thermoplastic polyurethaneis based on diphenylmethane diisocyanate (MDI).

Compounds (b) reactive toward isocyanates used may in principle be anysuitable compounds known to those skilled in the art. As compound (b)reactive toward isocyanates, in accordance with the invention, at leastone diol is used.

It is possible here in the context of the present invention to use anysuitable diols, for example polyether diols or polyester diols ormixtures of two or more thereof.

In principle, it is possible in accordance with the invention to use anysuitable polyester diols, the term “polyester diol” in the context ofthe present invention also comprising polycarbonatediols.

In one embodiment of the present invention, a polycarbonatediol or apolytetrahydrofuran polyol is used. Suitable polytetrahydrofuran polyolshave, for example, a molecular weight in the range from 500 to 5000g/mol, preferably 500 to 2000 g/mol, more preferably 800 to 1200 g/mol.

Suitable polycarbonatediols are, for example, polycarbonatediols basedon alkanediols. Suitable polycarbonatediols are strictly difunctionalOH-functional polycarbonatediols, preferably strictly difunctionalOH-functional aliphatic polycarbonatediols. Suitable polycarbonatediolsare based, for example, on butane-1,4-diol, pentane-1,5-diol orhexane-1,6-diol, especially butane-1,4-diol, pentane-1,5-diol,hexane-1,6-diol, 3-methylpentane-1,5-diol or mixtures thereof, morepreferably butane-1,4-diol, pentane-1,5-diol, hexane-1,6-diol ormixtures thereof. Preference is given in the context of the presentinvention to using polycarbonatediols based on butane-1,4-diol andhexane-1,6-diol, polycarbonatediols based on pentane-1,5-diol andhexane-1,6-diol, polycarbonatediols based on hexane-1,6-diol, andmixtures of two or more of these polycarbonatediols.

The compositions of the invention preferably comprise at least onethermoplastic polyurethane selected from the group consisting ofthermoplastic polyurethanes based on at least one diisocyanate and atleast one polycarbonatediol and thermoplastic polyurethanes based on atleast one diisocyanate and polytetrahydrofuran polyol. Accordingly, thepolyurethanes present in the compositions of the invention are preparedusing, as component (b), at least one polycarbonatediol or apolytetrahydrofuran polyol.

In a further embodiment, the present invention therefore relates to acomposition as described above, wherein the thermoplastic polyurethaneis selected from the group consisting of thermoplastic polyurethanesbased on at least one diisocyanate and at least one polycarbonatediol,and thermoplastic polyurethanes based on at least one diisocyanate andpolytetrahydrofuran polyol.

In a further embodiment, the present invention also relates to acomposition as described above, wherein the thermoplastic polyurethaneis a thermoplastic polyurethane based on at least one diisocyanate andat least one polycarbonatediol. Preferably, the polycarbonatediols usedhave a number-average molecular weight Mn in the range from 500 to 4000g/mol, determined via GPC, preferably in the range from 650 to 3500g/mol, determined via GPC, more preferably in the range from 800 to 3000g/mol, determined via GPC.

The present invention further relates, in a further embodiment, also toa composition as described above, wherein the thermoplastic polyurethaneis a thermoplastic polyurethane based on at least one diisocyanate andat least one polycarbonatediol and the at least one polycarbonatediol isselected from the group consisting of polycarbonatediols based onbutane-1,4-diol and hexane-1,6-diol, polycarbonatediols based onpentane-1,5-diol and hexane-1,6-diol, polycarbonatediols based onhexane-1,6-diol, and mixtures of two or more of thesepolycarbonatediols. Further preferred are copolycarbonatediols based onthe diols pentane-1,5-diol and hexane-1,6-diol, preferably having amolecular weight Mn of about 2000 g/mol.

In a further embodiment, the present invention therefore relates to acomposition as described above, wherein the polycarbonatediol has anumber-average molecular weight Mn in the range from 500 to 4000 g/mol,determined via GPC, preferably in the range from 1000 to 3500 g/mol,determined via GPC, further preferably in the range from 1500 to 3000g/mol, determined via GPC.

Chain extenders (c) used may preferably be aliphatic, araliphatic,aromatic and/or cycloaliphatic compounds having a molecular weight of0.05 kg/mol to 0.499 kg/mol, preferably difunctional compounds, forexample diamines and/or alkanediols having 2 to 10 carbon atoms in thealkylene radical, di-, tri-, tetra-, penta-, hexa-, hepta-, octa-, nona-and/or decaalkylene glycols having 3 to 8 carbon atoms, especially1,2-ethylene glycol, propane-1,3-diol, butane-1,4-diol, hexane-1,6-diol,preferably corresponding oligo- and/or polypropylene glycols, where itis also possible to use mixtures of the chain extenders. Preferably, thecompounds (c) have only primary hydroxyl groups; most preferred isbutane-1,4-diol.

Catalysts (d) which accelerate particularly the reaction between the NCOgroups of the diisocyanates (a) and the hydroxyl groups of the compound(b) reactive toward isocyanates and the chain extender (c), in apreferred embodiment, are tertiary amines, especially triethylamine,dimethylcyclohexylamine, N-methylmorpholine, N,N′-dimethylpiperazine,2-(dimethylaminoethoxy)ethanol, diazabicyclo[2.2.2]octane; in anotherpreferred embodiment, these are organic metal compounds such as titanicesters, iron compounds, preferably iron(III) acetylacetonate, tincompounds, preferably tin diacetate, tin dioctoate, tin dilaurate or thedialkyltin salts of aliphatic carboxylic acids, preferably dibutyltindiacetate, dibutyltin dilaurate, or bismuth salts in which bismuth ispreferably in the 2 or 3 oxidation state, especially 3. Preference isgiven to salts of carboxylic acids. Carboxylic acids used are preferablycarboxylic acids having 6 to 14 carbon atoms, more preferably having 8to 12 carbon atoms. Examples of suitable bismuth salts are bismuth(III)neodecanoate, bismuth 2-ethylhexanoate and bismuth octanoate.

The catalysts (d) are preferably used in amounts of 0.0001 to 0.1 partby weight per 100 parts by weight of the compound (b) reactive withisocyanates. Preference is given to using tin catalysts, especially tindioctoate.

As well as catalysts (d), it is also possible to add customaryauxiliaries (e) to the formation components (a) to (c). Examples includesurface-active substances, fillers, further flame retardants, nucleatingagents, oxidation stabilizers, gliding and demolding aids, dyes andpigments, optionally stabilizers, for example against hydrolysis, light,heat or discoloration, inorganic and/or organic fillers, reinforcingagents and plasticizers. Suitable auxiliaries and additives can befound, for example, in the Kunststoffhandbuch [Plastics Handbook],volume VII, published by Vieweg and Hochtlen, Carl Hanser Verlag, Munich1966 (p. 103-113).

Suitable preparation processes for thermoplastic polyurethanes aredisclosed, for example, in EP 0 922 552 A1, DE 101 03 424 A1 or WO2006/072461 A1. The preparation is typically effected in a belt systemor a reaction extruder, but can also be effected on the laboratoryscale, for example in a manual casting method. Depending on the physicalproperties of the components, they are all mixed directly with oneanother or individual components are premixed and/or prereacted, forexample to give prepolymers, and only then subjected to polyaddition. Ina further embodiment, a thermoplastic polyurethane is first preparedfrom the formation components, optionally together with catalyst, intowhich auxiliaries may optionally also be incorporated. In that case, atleast one flame retardant is introduced into this material anddistributed homogeneously. The homogeneous distribution is preferablyeffected in an extruder, preferably in a twin-shaft extruder. To adjustthe hardness of the TPUs, the amounts used of formation components (b)and (c) can be varied within relatively broad molar ratios, typicallywith rising hardness as the content of chain extender (c) increases.

For preparation of thermoplastic polyurethanes, for example those havinga Shore A hardness of less than 95, preferably of 95 to 80 Shore A, morepreferably about 85 A, it is possible, for example, to use theessentially difunctional polyhydroxyl compounds (b) and chain extenders(c) advantageously in molar ratios of 1:1 to 1:5, preferably 1:1.5 to1:4.5, such that the resulting mixtures of the formation components (b)and (c) have a hydroxyl equivalent weight of greater than 200 andespecially of 230 to 450, whereas, for preparation of harder TPUs, forexample those having a Shore A hardness of greater than 98, preferablyof 55 to 75 Shore D, the molar ratios of (b):(c) are in the range from1:5.5 to 1:15, preferably from 1:6 to 1:12, such that the mixtures of(b) and (c) obtained have a hydroxyl equivalent weight of 110 to 200,preferably of 120 to 180.

In a further embodiment, the present invention therefore relates to acomposition as described above, wherein the thermoplastic polyurethanehas a Shore hardness in the range from 80 A to 100 A, determined inaccordance with DIN 53505.

To prepare the thermoplastic polyurethanes of the invention, theformation components (a), (b) and (c) are preferably reacted in thepresence of catalysts (d) and optionally auxiliaries and/or additives(e) in such amounts that the ratio of equivalents of NCO groups in thediisocyanates (a) to the sum total of the hydroxyl groups in theformation components (b) and (c) is 0.9 to 1.1:1, preferably 0.95 to1.05:1 and especially about 1.0 to 1.04:1.

The composition of the invention comprises the at least onethermoplastic polyurethane in an amount in the range from 30% by weightto 75% by weight, based on the overall composition, especially in therange from 35% by weight to 75% by weight, based on the overallcomposition, preferably in the range from 40% by weight to 70% byweight, further preferably in the range from 45% by weight to 65% byweight and especially preferably in the range from 50% by weight to 60%by weight, based in each case on the overall composition.

In a further embodiment, the present invention therefore relates to acomposition as described above, wherein the proportion of thethermoplastic polyurethane in the composition is in the range from 30%by weight to 75% by weight based on the overall composition.

The sum of all components of each composition adds up to 100% by weight.

Preference is given in accordance with the invention to preparingthermoplastic polyurethanes in which the thermoplastic polyurethane hasa mean molecular weight (M_(W)) in the range from 50 000 to 500 000 Da.The upper limit for the mean molecular weight (M_(W)) of thethermoplastic polyurethanes is generally determined by theprocessability, and also the spectrum of properties desired. Furtherpreferably, the thermoplastic polyurethane has a mean molecular weight(M_(W)) in the range from 75 000 to 400 000 Da, especially preferably inthe range from 100 000 to 300 000 Da.

In a further embodiment, the present invention therefore relates to acomposition as described above, wherein the thermoplastic polyurethanehas a mean molecular weight (M_(W)) in the range from 50 000 to 500 000Da.

The compositions of the invention comprise, as well as the at least onethermoplastic polyurethane and melamine cyanurate, a combination of twophosphorus-containing flame retardants (F1) and (F2). The compositionsof the invention comprise at least one first phosphorus-containing flameretardant (F1) selected from the group consisting of alkyl esters ofphosphoric acid and alkyl esters of phosphonic acid, where the alkylradicals are selected from C1 to C12 alkyl radicals, and at least onefurther phosphorus-containing flame retardant (F2) selected from thegroup consisting of derivatives of phosphinic acid.

According to the invention, the phosphorus-containing flame retardant(F1) is selected from the group consisting of alkyl esters of phosphoricacid and alkyl esters of phosphonic acid, where the alkyl radicals areselected from C1 to C12 alkyl radicals. For example, thephosphorus-containing flame retardant (F1) is selected from the groupconsisting of alkyl esters of phosphoric acid, where the alkyl radicalsare selected from C1 to C12 alkyl radicals. Alternatively, thephosphorus-containing flame retardant (F1) may be selected from thegroup consisting of alkyl esters of phosphonic acid, where the alkylradicals are selected from C1 to C12 alkyl radicals.

If the ester comprises more than one alkyl radical, the alkyl radicalsmay be the same or different. According to the invention, the alkylradicals may be substituted or unsubstituted, for example halogenated.The alkyl radicals may be linear, branched or cyclic. In a preferredembodiment, the alkyl radicals are selected from C1 to C8 alkylradicals, further preferably selected from C1 to C6 alkyl radicals.

Accordingly, the phosphorus-containing flame retardant (F1) ispreferably selected from the group consisting of alkyl esters ofphosphoric acid and alkyl esters of phosphonic acid, where the alkylradicals are selected from C1 to C8 alkyl radicals. Further preferably,the phosphorus-containing flame retardant (F1) is preferably selectedfrom the group consisting of alkyl esters of phosphoric acid and alkylesters of phosphonic acid, where the alkyl radicals are selected from C1to C6 alkyl radicals. In a further embodiment, the phosphorus-containingflame retardant (F1) is selected from the group consisting of alkylesters of phosphoric acid, where the alkyl radicals are selected from C1to C8 alkyl radicals, preferably selected from C1 to C6 alkyl radicals.In an alternative embodiment, the phosphorus-containing flame retardant(F1) is selected from the group consisting of alkyl esters of phosphonicacid, where the alkyl radicals are selected from C1 to C8 alkylradicals, preferably selected from C1 to C6 alkyl radicals.

In a further preferred embodiment, the phosphorus-containing flameretardant (F1) is liquid at 21° C.

Preferably, the flame retardant (F1) comprises salts having an organicor inorganic cation or organic esters. Organic esters are derivatives ofthe phosphorus-containing acids in which at least one oxygen atom bondeddirectly to the phosphorus has been esterified with an organic radical.In a preferred embodiment, the organic ester is a dialkyl ester, and inanother preferred embodiment a trialkyl ester. More preferably, allhydroxyl groups of the corresponding phosphorus-containing acid havebeen esterified.

In a further embodiment, the present invention therefore relates to acomposition as described above, wherein the phosphorus-containing flameretardant (F1) is a trialkyl phosphate where the alkyl radicals areselected from C1 to C12 alkyl radicals.

Suitable alkyl radicals are, for example, methyl groups, ethyl groups,propyl groups, butyl groups, pentyl groups, hexyl groups, heptyl groupsor octyl groups.

Organic phosphate esters are preferably the triesters of phosphoricacid, such as trialkyl phosphates. A suitable example in accordance withthe invention is tris-(2-ethylhexyl) phosphate.

The organic phosphonates are salts with an organic or inorganic cationor the esters of phosphonic acid. Preferred esters of phosphonic acidare the diesters of alkyl phosphonic acids. Suitable alkyl radicals arethose mentioned above.

Phosphonates suitable in accordance with the invention are, for example,methanephosphonates or spirophosphonates such as phosphonates of thegeneral formula (I):

where A¹ and A² are independently a linear or branched alkyl radicalhaving 1 to 4 carbon atoms, for example a linear or branched alkylradical having 2 to 4 carbon atoms, preferably a methyl group, an ethylgroup, an n-propyl group, an i-propyl group, an n-butyl group, ani-butyl group or a t-butyl group, further preferably a methyl group.

Accordingly, the present invention also relates, in a furtherembodiment, to a composition as described above, wherein thephosphorus-containing flame retardant (F1) is selected from the groupconsisting of trialkyl phosphates, methanephosphonates and phosphonatesof the general formula (I):

where A¹ and A² are independently a linear or branched alkyl radicalhaving 1 to 4 carbon atoms, preferably a methyl group.

In a further embodiment, the present invention also relates to acomposition as described above, wherein the phosphorus-containing flameretardant (F1) is tris(2-ethylhexyl) phosphate.

In a further embodiment, the present invention also relates to acomposition as described above, wherein the phosphorus-containing flameretardant (F1) is dimethyl spirophosphate.

The proportion of the flame retardant (F1) in the composition of theinvention is, for example, in the range from 2% to 15% by weight, basedon the overall composition, preferably in the range from 3% to 10% byweight, based on the overall composition, especially in the range from5% to 8% by weight, based on the overall composition.

In a further embodiment, the present invention therefore relates to acomposition as described above, wherein the proportion of the flameretardant (F1) is in the range from 2% to 15% based on the overallcomposition.

Preferably, the flame retardant (F2) selected from derivatives ofphosphinic acid comprises salts with an organic or inorganic cation ororganic esters. Organic esters are derivatives of phosphinic acid inwhich at least one oxygen atom bonded directly to the phosphorus hasbeen esterified with an organic radical. In a preferred embodiment, theorganic ester is an alkyl ester, and in another preferred embodiment anaryl ester. More preferably, all hydroxyl groups of the phosphinic acidhave been esterified.

Phosphinic esters have the general formula R¹R²(P═O)OR³ where all threeorganic groups R¹, R² and R³ may be the same or different. The R¹, R²and R³ radicals are either aliphatic or aromatic and have 1 to 20 carbonatoms, preferably 1 to 10 and further preferably 1 to 3.

Preferably, at least one of the radicals is aliphatic, preferably allthe radicals are aliphatic, and most preferably R¹ and R² are ethylradicals. Further preferably, R³ is also an ethyl radical or a methylradical. In a further preferred embodiment, R¹, R² and R³ aresimultaneously ethyl radical or methyl radicals.

Preference is also given to phosphinates, i.e. the salts of phosphinicacid. The R¹ and R² radicals are either aliphatic or aromatic and have 1to 20 carbon atoms, preferably 1 to 10 and further preferably 1 to 3.Preferably, at least one of the radicals is aliphatic, preferably allthe radicals are aliphatic, and most preferably R¹ and R² are ethylradicals. Preferred salts of phosphinic acids are aluminum salts,calcium salts or zinc salts, further preferably aluminum salts or zincsalts. A preferred embodiment is diethylaluminum phosphinate.

In a further embodiment, the present invention therefore relates to acomposition as described above, wherein the phosphorus-containing flameretardant (F2) is a phosphinate.

In a further embodiment, the present invention therefore relates to acomposition as described above, wherein the phosphinate is selected fromthe group consisting of aluminum phosphinates and zinc phosphinates.

The proportion of the flame retardant (F2) in the composition of theinvention is, for example, in the range from 3% to 15% by weight, basedon the overall composition, especially 5% to 15% by weight, based on theoverall composition, preferably in the range from 7% to 13% by weight,based on the overall composition, especially in the range from 9% to 11%by weight, based on the overall composition.

In a further embodiment, the present invention therefore relates to acomposition as described above, wherein the proportion of the flameretardant (F2) in the composition is in the range from 3% to 15% byweight based on the overall composition.

In one embodiment, for preparation of the compositions of the invention,thermoplastic polyurethane, melamine cyanurate and flame retardants (F1)and (F2) are processed in one step. In other preferred embodiments, forpreparation of the compositions of the invention, a reaction extruder, abelt system or other suitable apparatus is firstly used to prepare athermoplastic polyurethane, preferably in pellet form, into whichmelamine cyanurate and the flame retardants (F1) and (F2) are thenintroduced in at least one further step, or else two or more steps.

The mixing of the thermoplastic polyurethane with the other componentsis effected in a mixing unit which is preferably an internal kneader oran extruder, preferably a twin-shaft extruder. In a preferredembodiment, at least one flame retardant introduced into the mixing unitin the at least one further step is in liquid form, i.e. in liquid format a temperature of 21° C. In another preferred embodiment of the use ofan extruder, the flame retardant introduced is at least partly liquid ata temperature that exists behind the intake point in flow direction ofthe material charge in the extruder.

According to the invention, the composition may comprise further flameretardants, for example including phosphorus-containing flameretardants. Preferably, the composition of the invention, however, asidefrom the melamine cyanurate and the phosphorus-containing flameretardants (F1) and (F2), does not comprise any further flameretardants.

The combination of the various flame retardants optimizes mechanicalproperties and flame retardancy properties in accordance with theinvention.

In this case, the mass ratio of the sum total of thephosphorus-containing flame retardants (F1) and (F2) present in thecomposition to the melamine cyanurate present in the composition, inaccordance with the invention, is in the range from 1:3 to 1:1, forexample in the region of 1:2.

Accordingly, the present invention, in a further embodiment, alsorelates to a composition comprising at least one thermoplasticpolyurethane, at least melamine cyanurate, at least one firstphosphorus-containing flame retardant (F1) selected from the groupconsisting of alkyl esters of phosphoric acid and alkyl esters ofphosphonic acid, where the alkyl radicals are selected from C1 to C12alkyl radicals, and at least one further phosphorus-containing flameretardant (F2) selected from the group consisting of derivatives ofphosphinic acid, wherein

-   -   the proportion of the thermoplastic polyurethane in the        composition is in the range from 30% to 75% by weight,    -   the proportion of the melamine cyanurate in the composition is        in the range from 20% to 40% by weight,    -   the proportion of the flame retardant (F2) in the composition is        in the range from 3% to 15% by weight, and    -   the proportion of the flame retardant (F1) is in the range from        2% to 15% by weight,        based in each case on the overall composition, where the sum        total of the components of the composition is 100% by weight.

According to the invention, the composition may comprise furtherconstituents, for example standard auxiliaries and additives forthermoplastic polyurethanes. Preferably, the composition, aside from themelamine cyanurate, the at least one phosphorus-containing flameretardant (F1) and the at least one phosphorus-containing flameretardant (F2), does not comprise any further flame retardants. Furtherpreferably, the composition of the invention comprises melaminecyanurate, exactly one phosphorus-containing flame retardant (F1)selected from the group consisting of alkyl esters of phosphoric acidand alkyl esters of phosphonic acid, where the alkyl radicals areselected from C1 to C12 alkyl radicals, and exactly onephosphorus-containing flame retardant (F2) selected from the groupconsisting of derivatives of phosphinic acid.

The present invention also relates to the use of the composition of theinvention comprising at least one flame-retardant thermoplasticpolyurethane as described above for production of coatings, dampingelements, bellows, films or fibers, shaped bodies, floors for buildingsand transport, nonwovens, preferably seals, rollers, shoe soles, hoses,cables, cable connectors, cable sheaths, cushions, laminates, profiles,belts, saddles, foams, plug connectors, trailing cables, solar modules,automobile trim. Preference is given to the use for production of cablesheaths. The production is preferably effected from pellets, byinjection molding, calendering, powder sintering or extrusion and/or byadditional foaming of the composition of the invention.

Accordingly, the present invention also relates to the use of acomposition comprising at least one thermoplastic polyurethane, at leastmelamine cyanurate, at least one first phosphorus-containing flameretardant (F1) selected from the group consisting of derivatives ofphosphoric acid and derivatives of phosphonic acid and at least onefurther phosphorus-containing flame retardant (F2) selected from thegroup consisting of derivatives of phosphinic acid as described abovefor production of cable sheaths.

Further embodiments of the present invention can be inferred from theclaims and the examples. It will be appreciated that the features of theinventive subject matter/process or of the inventive uses which havebeen mentioned above and those elucidated below can be used not only inthe combination specified in each case but also in other combinations,without leaving the scope of the invention. For example, the combinationof a preferred feature with an especially preferred feature or of afeature which is not characterized any further with an especiallypreferred feature, etc., is implicitly also encompassed even if thiscombination is not mentioned explicitly.

Listed hereinafter are illustrative embodiments of the presentinvention, though these do not restrict the present invention. Moreparticularly, the present invention also encompasses those embodimentswhich arise from the dependency references and hence combinationsspecified hereinafter.

-   1. A composition comprising at least one thermoplastic polyurethane,    at least melamine cyanurate, at least one first    phosphorus-containing flame retardant (F1) selected from the group    consisting of alkyl esters of phosphoric acid and alkyl esters of    phosphonic acid, where the alkyl radicals are selected from C1 to    C12 alkyl radicals, and at least one further phosphorus-containing    flame retardant (F2) selected from the group consisting of    derivatives of phosphinic acid.-   2. The composition according to embodiment 1, wherein the    phosphorus-containing flame retardant (F2) is a phosphinate.-   3. The composition according to embodiment 2, wherein the    phosphinate is selected from the group consisting of aluminum    phosphinates and zinc phosphinates.-   4. The composition according to any of embodiments 1 to 3, wherein    the phosphorus-containing flame retardant (F1) is a trialkyl    phosphate where the alkyl radicals are selected from C1 to C12 alkyl    radicals.-   5. The composition according to any of embodiments 1 to 3, wherein    the flame retardant (F1) is selected from the group consisting of    trialkyl phosphates, methanephosphonates and phosphonates of the    general formula (I):

-   -   where A¹ and A² are independently a linear or branched alkyl        radical having 1 to 4 carbon atoms.

-   6. The composition according to any of embodiments 1 to 5, wherein    the melamine cyanurate has a particle size in the range from 0.1 to    100 μm.

-   7. The composition according to any of embodiments 1 to 6, wherein    the thermoplastic polyurethane is selected from the group consisting    of thermoplastic polyurethanes based on at least one diisocyanate    and at least one polycarbonatediol, and thermoplastic polyurethanes    based on at least one diisocyanate and polytetrahydrofuran polyol.

-   8. The composition according to any of embodiments 1 to 7, wherein    the thermoplastic polyurethane has a mean molecular weight (M_(W))    in the range from 50 000 to 500 000 Da.

-   9. The composition according to any of embodiments 1 to 8, wherein    the thermoplastic polyurethane is based on diphenylmethane    diisocyanate (MDI).

-   10. The composition according to any of embodiments 1 to 9, wherein    the thermoplastic polyurethane has a Shore hardness in the range    from 80 A to 100 A, determined in accordance with DIN 53505.

-   11. The composition according to any of embodiments 1 to 10, wherein    the proportion of the thermoplastic polyurethane in the composition    is in the range from 30% by weight to 75% by weight based on the    overall composition.

-   12. The composition according to any of embodiments 1 to 11, wherein    the proportion of the melamine cyanurate in the composition is in    the range from 20% to 40% by weight based on the overall    composition.

-   13. The composition according to any of embodiments 1 to 12, wherein    the proportion of the flame retardant (F2) in the composition is in    the range from 3% to 15% by weight based on the overall composition.

-   14. The composition according to any of embodiments 1 to 13, wherein    the proportion of the flame retardant (F1) is in the range from 2%    to 15% by weight based on the overall composition.

-   15. The use of a composition according to any of embodiments 1 to 14    for production of cable sheaths.

-   16. A composition comprising at least one thermoplastic    polyurethane, at least melamine cyanurate, at least one first    phosphorus-containing flame retardant (F1) selected from the group    consisting of alkyl esters of phosphoric acid, where the alkyl    radicals are selected from C1 to C12 alkyl radicals and at least one    further phosphorus-containing flame retardant (F2) selected from the    group consisting of derivatives of phosphinic acid.

-   17. The composition according to embodiment 16, wherein the    phosphorus-containing flame retardant (F2) is a phosphinate.

-   18. The composition according to embodiment 17, wherein the    phosphinate is selected from the group consisting of aluminum    phosphinates and zinc phosphinates.

-   19. The composition according to any of embodiments 16 to 18,    wherein the phosphorus-containing flame retardant (F1) is a trialkyl    phosphate where the alkyl radicals are selected from C1 to C12 alkyl    radicals.

-   20. The composition according to any of embodiments 16 to 19,    wherein the flame retardant (F1) is selected from the group    consisting of trialkyl phosphates.

-   21. The composition according to any of embodiments 16 to 20,    wherein the melamine cyanurate has a particle size in the range from    0.1 to 100 μm.

-   22. The composition according to any of embodiments 16 to 21,    wherein the thermoplastic polyurethane is selected from the group    consisting of thermoplastic polyurethanes based on at least one    diisocyanate and at least one polycarbonate diol, and thermoplastic    polyurethanes based on at least one diisocyanate and    polytetrahydrofuran polyol.

-   23. The composition according to any of embodiments 16 to 22,    wherein the thermoplastic polyurethane has an average molecular    weight (M_(W)) in the range from 50 000 to 500 000 Da.

-   24. The composition according to any of embodiments 16 to 23,    wherein the thermoplastic polyurethanes based on diphenylmethane    diisocyanate (MDI).

-   25. The composition according to any of embodiments 16 to 24,    wherein the thermoplastic polyurethane has a Shore hardness in the    range from 80 A to 100 A, determined according to DIN 53505.

-   26. The composition according to any of embodiments 16 to 25,    wherein the proportion of the thermoplastic polyurethane in the    composition is in the range from 30% to 75% by weight based on the    overall composition.

-   27. The composition according to any of embodiments 16 to 26,    wherein the proportion of the melamine cyanurate in the composition    is in the range from 20% to 40% by weight based on the overall    composition.

-   28. The composition according to any of embodiments 16 to 27,    wherein the proportion of the flame retardant (F2) in the    composition is in the range from 3% to 15% by weight based on the    overall composition.

-   29. The composition according to any of embodiments 16 to 28,    wherein the proportion of the flame retardant (F1) is in the range    from 2% to 15% by weight based on the overall composition.

-   30. The use of a composition according to any of embodiments 16 to    29 for production of cable sheaths.

-   31. A composition comprising at least one thermoplastic    polyurethane, at least melamine cyanurate, at least one first    phosphorus-containing flame retardant (F1) selected from the group    consisting of alkyl esters of phosphoric acid and alkyl esters of    phosphonic acid, where the alkyl radicals are selected from C1 to    C12 alkyl radicals, and at least one further phosphorus-containing    flame retardant (F2) selected from the group consisting of    derivatives of phosphinic acid.

-   32. The composition according to embodiment 31, wherein the    phosphorus-containing flame retardant (F2) is a phosphinate.

-   33. The composition according to embodiment 32, wherein the    phosphinate is selected from the group consisting of aluminum    phosphinates and zinc phosphinates.

-   34. The composition according to any of embodiments 31 to 33,    wherein the flame retardant (F1) is selected from the group    consisting of methanephosphonates and phosphonates of the general    formula (I):

-   -   where A¹ and A² are independently a linear or branched alkyl        radical having 1 to 4 carbon atoms.

-   35. The composition according to any of embodiments 31 to 34,    wherein the melamine cyanurate has a particle size in the range from    0.1 to 100 μm.

-   36. The composition according to any of embodiments 31 to 35,    wherein the thermoplastic polyurethane is selected from the group    consisting of thermoplastic polyurethanes based on at least one    diisocyanate and at least one polycarbonate diol, and thermoplastic    polyurethanes based on at least one diisocyanate and    polytetrahydrofuran polyol.

-   37. The composition according to any of embodiments 31 to 36,    wherein the thermoplastic polyurethane has an average molecular    weight (M_(W)) in the range from 50 000 to 500 000 Da.

-   38. The composition according to any of embodiments 31 to 37,    wherein the thermoplastic polyurethane is based on diphenylmethane    diisocyanate (MDI).

-   39. The composition according to any of embodiments 31 to 38,    wherein the thermoplastic polyurethane has a Shore hardness in the    range from 80 A to 100 A, determined according to DIN 53505.

-   40. The composition according to any of embodiments 31 to 39,    wherein the proportion of the thermoplastic polyurethane in the    composition is in the range from 30% to 75% by weight, based on the    overall composition.

-   41. The composition according to any of embodiments 31 to 40,    wherein the proportion of the melamine cyanurate in the composition    is in the range from 20% to 40% by weight, based on the overall    composition.

-   42. The composition according to any of embodiments 31 to 41,    wherein the proportion of the flame retardant (F2) in the    composition is in the range from 3% to 15% by weight, based on the    overall composition.

-   43. The composition according to any of embodiments 31 to 42,    wherein the proportion of the flame retardant (F1) is in the range    from 2% to 15% by weight based on the overall composition.

-   44. The use of a composition according to any of embodiments 31 to    43 for production of cable sheaths.

The examples which follow serve to illustrate the invention, but are inno way restrictive with respect to the subject matter of the presentinvention.

EXAMPLES

The examples show the good mechanical properties have, good flameretardancy properties show, simultaneously good mechanical and chemicalstability have, and are additionally discolored to a minor degree, if atall, when subjected to UV radiation.

1. Feedstocks

-   -   Elastollan 1185A10: TPU of Shore hardness 85 A from BASF        Polyurethanes GmbH, Elastogranstrasse 60, 49448 Lemforde, based        on polytetrahydrofuran polyol (PTHF) having a molecular weight        of 1000, butane-1,4-diol, MDI.    -   Melapur MC 15 ED: Melamine cyanurate        (1,3,5-triazine-2,4,6(1H,3H,5H)-trione, compound with        1,3,5-triazine-2,4,6-triamine (1:1)), CAS #: 37640-57-6, BASF        SE, 67056 Ludwigshafen, GERMANY, particle size D99%<1=50 μm,        D50%<=4.5 μm, water content % (w/w)<0.2.    -   Fyrolflex RDP: Resorcinol bis(diphenylphosphate), CAS #:        125997-21-9, Supresta Netherlands B.V., Office Park De Hoef,        Hoefseweg 1, 3821 AE Amersfoort, the Netherlands, viscosity at        25° C.=700 mPas, acid number<0.1 mg KOH/g, water content %        (w/w)<0.1.    -   Exolit OP 1230: Aluminum diethylphosphinate, CAS#: 225789-38-8,        Clariant Produkte (Deutschland) GmbH, Chemiepark Knapsack, 50351        Hürth, water content % (w/w)<0.2, average particle size (D50)        20-40 μm.    -   Chisorb 622 LT: dimethyl butandioate, polymer with        4-hydroxy-2,2,6,6-tetramethyl-1-piperidinethanol, CAS #:        65447-77-0, BASF Polyurethanes GmbH, Postfach 1140, 49440        Lemfoerde, GERMANY.    -   Tinuvin 234:        2-(2H-benzzotriazol-2-yl)4,6-bis(1-ethyl-1-phenylethylphenol),        CAS #: 70321-86-17, BASF SE, 67056 Ludwigshafen, GERMANY.    -   Disflamoll TOF: tris(2-ethylhexyl) phosphate, CAS #78-42-2,        LANXESS Deutschland GmbH, 51369 Leverkusen.

2. Production of the Mixtures

-   -   Table 1 below lists compositions in which the individual        constituents are stated in parts by weight (PVV). The mixtures        were each produced with a Berstorff ZE 40 A twin-screw extruder        having a screw length of 35 D divided into 10 barrel sections.

TABLE 1 Composition 1 (CE) 2 (CE) 3 1185A10 56.2 55 55 Disflamoll TOF 5Fyroflex RDP 5 5 Melapur 15 ED 29.8 29.8 29.8 Exolit OP 1230 9 9 9Tinuvin 234 0.6 0.6 Chisorb 622 LT 0.6 0.6 (CE) comparative example

3. Mechanical Properties

-   -   The mixtures were extruded with an Arenz single-screw extruder        having a three-zone screw with a mixing section (screw ratio        1:3) to give films having a thickness of 1.6 mm. Density, Shore        hardness, tensile strength, tear propagation resistance,        abrasion and elongation at break of the corresponding test        specimens were measured. All compositions have good mechanical        properties. The results are compiled in table 2.

TABLE 2 Standard mechanical properties 1 (CE) 2 (CE) 3 Density [g/cm³]1.287 1.347 1.27 Shore A 92 89 91 Tensile strength [MPa] 15 14 14Elongation at break [%] 580 520 550 Tear propagation resistance [kN/m]57 55 50 Wear [mm³] 90 131 97 (CE) comparative example

Test Methods:

-   -   Density: DIN EN ISO 1183-1, A    -   Shore hardness A: DIN 53505

Tensile strength: DIN EN ISO 527

-   -   Elongation at break: DIN EN ISO 527    -   Tear propagation resistance: DIN ISO 34-1, B (b    -   Wear: DIN 53516

4. Discoloration on UV Exposure

-   -   The mixtures were extruded with an Arenz single-screw extruder        having a three-zone screw with a mixing section (screw ratio        1:3) to give films having a thickness of 1.6 mm. The delta E        values (ASTM E313) of the corresponding specimens were measured        after various exposure times by the method ASTM G155 Cy4. Lower        delta E values were found for the TPU mixtures of the invention.    -   The results are summarized in table 3.

TABLE 3 Illumination according to ASTM G155 Cy4 Time 1 (CE) 2 (CE) 3Color measurement in reflection 0 h (without specular reflection) Colorseparation delta E 0 0 0 Color measurement in reflection 0 h (withspecular reflection) Color separation delta E 0 0 0 Color measurement inreflection 100 h (without specular reflection) Color separation delta E4.8 1.9 1.1 Color measurement in reflection 100 h (with specularreflection) Color separation delta E 4.8 1.4 1.1 Color measurement inreflection 200 h (without specular reflection) Color separation delta E9.3 4.5 2.1 Color measurement in reflection 200 h (with specularreflection) Color separation delta E 9.3 4.4 2.1 Color measurement inreflection 300 h (without specular reflection) Color separation delta E14.9 8 3.1 Color measurement in reflection 300 h (with specularreflection) Color separation delta E 15 7.5 3.1 (CE) comparative example

-   -   A small value for delta E represents lower discoloration caused        by the test. The lower the discoloration in the test, the        smaller the discoloration to be expected in practical use, for        example under insolation.

The results show that the materials of the invention have improvedproperties, especially good long-term stability.

1. A composition comprising at least one thermoplastic polyurethane, atleast melamine cyanurate, at least one first phosphorus-containing flameretardant (F1) selected from the group consisting of alkyl esters ofphosphoric acid and alkyl esters of phosphonic acid, where the alkylradicals are selected from C1 to C12 alkyl radicals, and at least onefurther phosphorus-containing flame retardant (F2) selected from thegroup consisting of derivatives of phosphinic acid.
 2. The compositionaccording to claim 1, wherein the phosphorus-containing flame retardant(F2) is a phosphinate.
 3. The composition according to claim 2, whereinthe phosphinate is selected from the group consisting of aluminumphosphinates and zinc phosphinates.
 4. The composition according toclaim 1, wherein the phosphorus-containing flame retardant (F1) is atrialkyl phosphate where the alkyl radicals are selected from C1 to C12alkyl radicals.
 5. The composition according to claim 1, wherein theflame retardant (F1) is selected from the group consisting of trialkylphosphates, methanephosphonates and phosphonates of formula (I):

where A¹ and A² are each independently a linear or branched alkylradical having 1 to 4 carbon atoms.
 6. The composition according toclaim 1, wherein the melamine cyanurate has a particle size in the rangefrom 0.1 to 100 μm.
 7. The composition according to claim 1, wherein thethermoplastic polyurethane is selected from the group consisting ofthermoplastic polyurethanes based on at least one diisocyanate and atleast one polycarbonatediol, and thermoplastic polyurethanes based on atleast one diisocyanate and polytetrahydrofuran polyol.
 8. Thecomposition according to claim 1, wherein the thermoplastic polyurethanehas a mean molecular weight (M_(W)) in a range from 50 000 to 500 000Da.
 9. The composition according to claim 1, wherein the thermoplasticpolyurethane is based on diphenylmethane diisocyanate (MDI).
 10. Thecomposition according to claim 1, wherein the thermoplastic polyurethanehas a Shore hardness in a range from 80 A to 100 A, determined inaccordance with DIN
 53505. 11. The composition according to claim 1,wherein a proportion of the thermoplastic polyurethane in thecomposition is in a range from 30% to 75% by weight based on the overallcomposition.
 12. The composition according to claim 1, wherein aproportion of the melamine cyanurate in the composition is in a rangefrom 20% to 40% by weight based on the overall composition.
 13. Thecomposition according to claim 1, wherein a proportion of the flameretardant (F2) in the composition is in a range from 3% to 15% by weightbased on the overall composition.
 14. The composition according to claim1, wherein a proportion of the flame retardant (F1) is in a range from2% to 15% by weight based on the overall composition.
 15. A cable sheathcomprising the composition according to claim 1.